1. Field of the Invention
This invention relates to a printing device such as a thermal printer or an electric discharging type printer, in which the printing is effected by urging a print head onto recording paper.
2. Description of Prior Art
Conventional printing devices such as a thermal printer, an electric discharging type printer, etc., wherein the printing is done by urging the print head onto recording paper, are of such a construction that, when the paper forwarding is done by manual operation, the print head is parted from the recording paper by a separate power source.
That is, as illustrated in FIG. 1 of the accompanying drawing, the print head 1 is slidably mounted on a guide rail 2, and a platen (or a pad) 3 is provided in parallel with the guide rail 2. Below the pad 3, there is extended a paper forwarding roller 4, by way of which recording paper 5 is led out onto the pad 3.
A lever 6 is fixedly provided at one end of the guide rail 2, and is constantly subjected to a clockwise rotational force by a coil spring 7, whereby the print head 1 is constantly urged to the pad 3 through the guide rail 2.
In case the printing device is a thermal printer, the print head 1 moves on the guide rail 2 in a state where its heat generating part is in contact with the recording paper 5, while performing the sequential printing by means of digit changing means such as a pulse motor, etc. (not shown).
When the printing for one line is terminated, the print head 1 is separated from the recording paper, and then returns to its original position. In order to thus keep the print head 1 away from the recording paper 5 at the time of its return to the original position or during a paper forwarding operation, a solenoid 8 to raise the print head 1 is provided on the lever 6. By this solenoid 8, the guide rail 2 is rotated counterclockwise to temporarily separate the print head 1 from the recording paper 5 so that the paper forwarding may be done during this temporary separation. Besides being operated at the time of the automatic paper forwarding, wherein the paper is forwarded by the pulse motor (not shown) through a power transmission gear 9 by the paper forwarding roller 4, this print head raising solenoid 8 is also operated at the time of manual paper forwarding. That is to say, a manually rotatable gear 10 to be meshed with the paper forwarding gear 9 is pivotally supported on a lever 11, which is constantly energized in a direction of separating the manually rotatable gear 10 from the power transmission gear 9 by a coil spring 12.
The manually rotatable gear 10, when it is rotated by an operator for the paper forwarding, is pushed downward and meshed with the power transmission gear 9 to rotate the paper forwarding roller 4. At this time, if the print head 1 is not away from the recording paper 5, jamming of the paper may occur. Therefore, a microswitch 13 to be actuated by the lever 11 which has been pushed down is provided beneath the lever so that the print head raising solenoid 8 may be actuated thereby. As a result of this, it becomes possible to regularly forward the paper even by the manual operation.
However, with the abovementioned construction, wherein the print head is separated from the recording paper by a power source such as the print head raising solenoid 8, when the paper is forwarded by the manual operation, there possibly arises serious disadvantages to be mentioned hereinbelow.
(1) Since the print head should be kept away from the recording paper, if no electric conduction to the solenoid is possible, i.e., if the power source switch is not turned on, the manual paper forwarding operation cannot be effected.
(2) The part such as the microswitch 13, etc. to turn on the solenoid 8 often tends to readily get into troubles such as insufficient contact, etc., thereby lowering the reliability of the device.